1. Field of the Invention
This invention relates to fluoride glasses for use in infrared optical systems, and, more particularly to hot-pressed fluoride glasses.
2. Description of the Prior Art
A great need exists for rugged, infrared transparent glasses capable of being inexpensively fabricated into fiber optic elements and optical components such as laser hoses, windows, prisms, and Faraday rotators. Crystalline materials are, of course, known that are transparent in the infrared portion of the spectrum. These materials, such as ZnSe, NaCl, KCl, are difficult to fabricate inexpensively, since they are either not readily castable or moldable into a variety of sizes and shapes, or they are quite readily attacked by ambient humidity. In oxide glasses, oxygen vibrational modes limit IR transmission to wavelengths shorter than 5 .mu.m.
In view of the deficiencies of presently available mid-IR transparent glasses, the development of a new family of fluoride-based vitreous materials with transmission extending to 7 to 8 .mu.m has elicited considerable interest. These fluoride glasses are typically synthesized from ZrF.sub.4 -BaF.sub.2, HfF.sub.4 -BaF.sub.2 and mixtures thereof; see, e.g., U.S. Pat. No. 4,141,741. These glasses are quite hard and strong and are generally resistant to corrosion by environmental moisture. Use of these materials in optical applications, however, has been somewhat limited by the effects of cutting, grinding, polishing and other mechanical working which deform and contaminate surfaces of high purity cast glasses.